Degradation Mechanism of Acidic Congo Red in Sunlight/Fe2+/S2O82- System

The present study aims to find the mechanism of the better performance of sunlight/Fe2+/persulphate oxidation on the bases of degradation of acidic Congo red. The major intermediate product formed from acidic Congo red was 3,4-naphthalene quinonoids imine-1-sulfonate, a kind of Quinonoids imine compound. It was found that the 3,4-naphthalene quinonoids imine-1-sulfonate can be degraded immediately under the irradiation of UV lights or sunlight, and the degradation effect under sunlight was superior to those under UV. It was photosensitive to visible light. Thus it happened in photosensitive reaction process under visible light and could produce singlet oxygen (O-1(2)) and the superoxide radical (O-2 center dot(-)). O-2 center dot(-) could promote the generation of hydroxyl radicals ((OH)-O-center dot) and sulfate radicals (SO4-center dot) in acidic environment, and subsequently cause increase of active substances in the system. Therefore, the sunlight/Fe2+/persulphate degradation method might be an attractive alternative technology for the treatment of industrial dye.